The present invention relates to an automatic sun visor device.
In the prior art, a sun visor device is arranged in a vehicle above the driver and front passenger seats to block light, such as sunlight, that enters the vehicle occupant compartment of the vehicle. The sun visor device prevents the incident light that enters the vehicle from reaching the position of the eyes of a vehicle occupant so that the vehicle occupant is not dazzled by the light. However, the intensity of the incident light and its incident angle constantly vary depending on the direction of the vehicle or the surrounding environment of the vehicle. Thus, the vehicle occupant is constantly required to adjust the sun visor device in accordance with such changes in the incident light. To simplify such adjustments, an automatic sun visor device has been proposed. The automatic sun visor device automatically adjusts the position and the light transmission state of a light shielding plate based on the illuminance or angle of the incident light.
Japanese Laid-Open Patent Publication No. 7-329566 describes a sun visor device including a first photosensor for detecting incident light, a second photosensor for detecting incident light at an angle differing from the angle of the incident light detected by the first photosensor, and a control circuit for detecting the incident angle of incident light based on a detection signal output from each photosensor. The sun visor device adjusts the position of a sun visor body so that the sun visor body blocks incident light so as to follow changes in the incident angle of the incident light when the illuminance of the incident light detected by each photosensor exceeds a predetermined value. The sun visor body moves to a retracted position when the illuminance of the incident light detected by each photosensor is less than the predetermined value.
Japanese Laid-Open Utility Model Publication No. 5-34013 describes a sun visor device including a liquid crystal panel, which functions as a belt-shaped sun visor body, arranged on an upper portion of a front glass for an automobile. The sun visor device includes a sunlight sensor arranged on a headrest of a passenger seat. The sun visor device controls the light transmission state of the liquid crystal panel based on the amount of direct sunlight sensed by the sunlight sensor.
Japanese Patent No. 3103270 describes a sun visor device including a light shielding plate, which functions as a sun visor body, arranged above, for example, a driver seat in a vehicle. The sun visor device includes a first photosensor arranged at a projection side of the light shielding plate and a second photosensor arranged at a retraction side of the light shielding plate. The sun visor device further includes a control circuit for controlling the position of the light shielding plate based on detection signals output from the first and second photosensors. The sun visor device automatically controls and positions the light shielding plate between the first and second photosensors.
Japanese Laid-Open Patent Publication No. 2002-211241 describes an automatic sun visor device including a plurality of visor regions, which functions as a sun visor body, formed on a vehicle window using liquid crystal. The automatic sun visor device further includes orientation sensors for detecting the intensity of incident light in predetermined directions and a reference illuminance sensor for detecting brightness at and around the window. The sun visor device uses a comparator to determine whether the incident light needs to be blocked in each visor region based on the intensity of the incident light detected by the corresponding orientation sensor. Further, when the value of a reference illuminance signal output from the reference illuminance sensor is high, the reference level used by the comparator to determine whether incident light needs to be blocked is automatically set to a high value. In this manner, the sun visor device refers to the brightness of the surroundings when determining whether to block light.
However, the device described in Japanese Laid-Open Patent Publication No. 7-329566 detects the incident angle when detecting incident light having an illuminance greater than or equal to a predetermined value. In comparison to when the incident light is direct sunlight having a high illuminance, the device does not as accurately detect the incident angle of incident light having illuminance that is in an intermediate illuminance range, such as light in a shaded location. Thus, when the sun visor body is adjusted to follow the incident angle of incident light in the intermediate illuminance range, the sun visor body may move frequently and annoy the vehicle occupant.
To prevent the sun visor body from following incident light having an intermediate illuminance, a threshold L0, used to determine an illuminance range in which the sun visor body is moved so as to follow an incident angle θ of incident light and an illuminance range for retracting the sun visor body, may be set at a relatively high value as shown in FIG. 8(B). However, when the illuminance of the incident light fluctuates around the threshold, such as when the incident light is sunlight passing through the leaves of trees, the sun visor body may move frequently in the retraction direction and thus annoy the vehicle occupant.
To prevent frequent movement of the sun visor body, the operation of the sun visor body may be delayed, and the sun visor body may be stopped for a certain period of time. However, the device would not be able to instantaneously widen the view of the vehicle occupant when, for example, the vehicle enters a dark location like a tunnel and the blocking of light becomes unnecessary.
In the case of the device described in Japanese Laid-Open Utility Model Publication 5-34013, the liquid crystal panel is set in a light blocking state when the output of the sunlight sensor exceeds a threshold and set in a light transmitting state when the output of the sunlight sensor remains less than the threshold for a predetermined period of time. However, even if the liquid crystal panel does not need to be set in the light blocking state, the liquid crystal panel is once set in the light blocking state even of the output of the sunlight sensor only temporarily exceeds the threshold. In this case, the liquid crystal panel does not return to the light transmitting state until the predetermined period elapses. This may annoy the vehicle occupant.
In the case of the device described in Japanese Patent No. 3103270, the output of the first and second photosensors frequently changes when the light receiving state of the photosensors frequently changes due to, trees or buildings. This frequently moves the light shielding plate and annoys the vehicle occupant.
In the same manner, in the case of the device described in Japanese Laid-Open Patent Publication No. 2002-211241, the determination of the comparator for blocking light also changes frequently when the output of each sensor changes frequently. Thus, when the light receiving state of each sensor changes frequently due to, for example, trees or buildings, the output of each sensor also changes frequently. As a result, the visor regions move frequently and annoy the vehicle occupant.